Hypothalamo-adenohypophysial Axis Flashcards
How large is the pituitary gland?
Size of a pea
What is the pituitary gland also known as?
Hypophysis
Where does the pituitary gland sit?
Under hypothalamus below brain in the Sella Turca (pituitary fossa)
What are the two sections of the pituitary?
Anterior: adenohypophysis
Posterior: neurohypophysis
What is the clinical relevence of the sella turca?
Any pituitary tumour will be restricted by the walls of the bony cavity
What are the embryological origins of the pituitary?
Anterior: Buccal cavity has extension that begins growing upwards
Posterior: Downward movement of material from the hypothalamus
Two tissues fuse and lose contact w/buccal cavity
What is the area that lies between the top of the pituitary stalk and the hypothalamus, and what is it?
Median Eminence - essentially a mass of arteries
What does the neurohypophysis mainly consist of?
Nerve axons, w/their cell bodies in the hypothalamus
Where does the median eminence receive its blood supply from?
Superior hypophysial artery
What are the capillaries in the median eminence known as?
Primary capillary plexus (fenestrated, lies outside of blood-brain barrier)
Where does blood from the primary capillary plexus go?
Through portal veins which run down the pituitary stalk and terminate in the adenohypophysis in the secondary capillary plexus
Where does the blood go after leaving the adenohypophysis?
Into the cavernous sinus then out via jugular veins
Describe the action of hypothalamic control over the pituitary:
Hypothalmic neurones secrete chemicals from their axons.
NOT NEUROTRANSMITTERS
STRAIGHT INTO BLOOD
Axons lie on the primary capillary plexus in the median eminence.
Portal veins carry messengers into anterior pituitary, where they bind to target cells
What are the five main types of anterior pituitary cells?
Somatotrophs Lactotrophs Thyrotrophs Gonadotrophs Corticotrophs
What hormones do somatotrophs produce?
Somatotrophin (growth hormone)
Which anterior pituitary cells produce LH and FSH?
Gonadotrophs
Give two examples of Protein hormones produced by the adenohypophysis:
Somatotrophin
Prolactin
Give three examples of glycoprotein hormones produced by the adenohypophysis:
Thyrotrophin
LH and FSH
Give an example of a polypeptide hormone produced by the adenohypophysis:
Corticotrophin
What do somatotrophs target?
General body tissues, particularly the liver
growth hormone
What does prolactin target?
Breasts in lactating women
What does corticotrophin target?
Adrenal cortex
What are the stimulatory/inhibitory hormones for Somatotrophin production?
Stim: Growth hormone releasing hormone
Inhib: Somatostatin
What are the stimulatory/inhibitory hormones for Prolactin production?
Stim: Thyrotrophin releasing hormone
Inhib: Dopamine (dominant over TRH)
What two hormones do Thryotrophin stimulating hormone stimulate?
Prolactin
Thyroid stimulating hormone
What are the two stimulatory hormones of ACTH?
Vasopressin
Corticotrophin releasing hormone
What type of hormones stimulate hormone release from the anterior pituitary?
Releasing hormones
What happens when Somatotrophin reaches the liver?
It stimulates the production of Insulin-like Growth Factor I and II (IGF1&2)
Where does IGF1 bind, and what effect does it have?
Receptors on Bone and Muscle
More protein synthesis
Increased gluconeogenesis
Stimulation of lipolysis to lead to increased fatty acid production
Cartilage and bone growth
Describe the negative feedback loop that inhibits Somatotrophin:
Direct IGF1 to the pituitary reduces secretion of somatotrophin
(or indirect via hypothalamus)
What is a physiological stimulus of Growth hormone secretion?
Hypoglycaemia, since IGF stimulates Gluconeogenesis etc.
What does Prolactin inhibit?
LH production
- as mainly present during lactation, so prevents periods and suppresses sexual behaviour, as mother would not want to become pregnant again
How is the synthesis of new milk started for the next suckling period?
Suckling stimulation of nipple stimulates afferent neural pathway to the hypothalamus.
This inhibits dopamine production, so more prolactin is released
